CentOS7的swap分區管理（分區或文件）

CentOS7的swap分區管理（分區或文件）

一、swap能夠在安裝操做系統的時候劃分單獨分區建立；也能夠安裝好操做系統後劃分剩餘硬盤建立；還能夠建立一個文件當swap分區使用

二、建議建立一個新的分區當swap使用，若是想使用一個文件當swap分區用的話最好將文件放在固態硬盤上，使用文件充當swap的話能夠隨意變大變小，移動也方便，但性能不如分區好

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建立分區來劃分swap

1、使用free -h查看當前swap

當前系統有4G的swap空間

[root@centos7 ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:           1.9G        180M        1.2G         19M        545M        1.6G
Swap:          4.0G         12M        4.0G

使用swapon -s顯示當前系統的swap

[root@centos7 ~]# swapon -s
Filename                Type        Size   Used Priority
/dev/dm-0                               partition   419430012676    -2

2、使用lsblk查看當前系統的硬盤

能夠看到，sda總共200G，如今才劃分了150多G，還有能夠用的空間

[root@centos7 ~]# lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda       8:0    0  200G  0 disk 
├─sda1    8:1    0    1G  0 part /boot
├─sda2    8:2    0  100G  0 part /
├─sda3    8:3    0   50G  0 part /data
├─sda4    8:4    0    1K  0 part 
└─sda5    8:5    0    4G  0 part 
  └─centos-swap
        253:0    0    4G  0 lvm  [SWAP]
sdb       8:16   0   20G  0 disk 
└─sdb2    8:18   0    2G  0 part

3、使用fdisk對/dev/sda硬盤進行建立分區操做

[root@centos7 ~]# fdisk /dev/sda
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): n
All primary partitions are in use
Adding logical partition 6
First sector (325072896-419430399, default 325072896): 
Using default value 325072896
Last sector, +sectors or +size{K,M,G} (325072896-419430399, default 419430399): +2G
Partition 6 of type Linux and of size 2 GiB is set

Command (m for help): p

Disk /dev/sda: 214.7 GB, 214748364800 bytes, 419430400 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000f14f7

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048     2099199     1048576   83  Linux
/dev/sda2         2099200   211814399   104857600   83  Linux
/dev/sda3       211814400   316671999    52428800   83  Linux
/dev/sda4       316672000   419430399    51379200    5  Extended
/dev/sda5       316674048   325070847     4198400   8e  Linux LVM
/dev/sda6       325072896   329267199     2097152   83  Linux

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

4、執行兩下partprobe(CentOS6執行part /dev/sda -a)

[root@centos7 ~]# partprobe 
Warning: Unable to open /dev/sr0 read-write (Read-only file system).  /dev/sr0 has been opened read-only.
Error: Invalid partition table - recursive partition on /dev/sr0.
Warning: Unable to open /dev/sr1 read-write (Read-only file system).  /dev/sr1 has been opened read-only.
[root@centos7 ~]# partprobe 
Warning: Unable to open /dev/sr0 read-write (Read-only file system).  /dev/sr0 has been opened read-only.
Error: Invalid partition table - recursive partition on /dev/sr0.
Warning: Unable to open /dev/sr1 read-write (Read-only file system).  /dev/sr1 has been opened read-only.

5、建立文件系統

[root@centos7 ~]# ls /dev/sda6
/dev/sda6
[root@centos7 ~]# mkswap /dev/sda6
Setting up swapspace version 1, size = 2097148 KiB
no label, UUID=b98996a2-a548-4266-b636-b2cb75cd0626

6、寫入/etc/fstab，並mount -a測試

[root@centos7 ~]# blkid /dev/sda6
/dev/sda6: UUID="b98996a2-a548-4266-b636-b2cb75cd0626" TYPE="swap"
[root@centos7 ~]# vim /etc/fstab 
[root@centos7 ~]# tail -1 /etc/fstab
UUID=b98996a2-a548-4266-b636-b2cb75cd0626 swap swap defaults 0 0
# 被掛載的設備名 掛載點 文件系統類型 掛載選項 轉儲頻率 系統自檢選項
[root@centos7 ~]# mount -a

7、swapon -a

此時執行free -h，swap分區還沒顯示出來，執行swapon -a，啓用全部swap

[root@centos7 ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:           1.9G        176M        1.2G         19M        547M        1.6G
Swap:          4.0G         12M        4.0G
# 執行swapon -a
[root@centos7 ~]# swapon -a
[root@centos7 ~]# free -h
              total        used        free      shared  buff/cache   available
Mem:           1.9G        178M        1.2G         19M        547M        1.6G
Swap:          6.0G         12M        6.0G

8、卸載這個swap

# 使用swapoff關閉/dev/sda6這個swap分區
[root@centos7 ~]# swapoff /dev/sda6
# 使用sed刪除fstab最後加的一行
[root@centos7 ~]# sed -ri '$d' /etc/fstab
# mount -a
[root@centos7 ~]# mount -a
# 此時swap已變成原來的4G

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建立一個文件充當swap分區

1、使用dd命令建立一個文件100M，當swap用

[root@centos7 data]# dd if=/dev/zero of=/data/swapfile bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 2.74665 s, 38.2 MB/s
# swap文件權限修改成600，安全
[root@centos7 data]# chmod 600 swapfile

2、對該文件建立文件系統

[root@centos7 data]# mkswap swapfile 
Setting up swapspace version 1, size = 102396 KiB
no label, UUID=a16538e7-685e-4141-aaeb-e1b7896cffdf

3、寫入/etc/fstab,掛載（這裏要注意，掛載設備不能寫UUID，只能寫文件名）

[root@centos7 data]# tail -1 /etc/fstab
/data/swapfile      swap            swap    defaults    0 0
[root@centos7 data]# mount -a

4、執行swapon -a 開啓全部swap

[root@centos7 data]# swapon -a
[root@centos7 data]# swapon -s
Filename                Type        Size    Used    Priority
/dev/dm-0                               partition   4194300 12672   -2
/data/swapfile                          file    102396  0   -3
[root@centos7 data]# free -h
              total        used        free      shared  buff/cache   available
Mem:           1.9G        176M        1.1G         19M        650M        1.6G
Swap:          4.1G         12M        4.1G

5、增大swap，須要先取消掛載

# 必須先卸載，否則報錯了
[root@centos7 data]# dd if=/dev/zero of=/data/swapfile bs=1M count=200
dd: failed to open ‘/data/swapfile’: Text file busy
# 卸載
[root@centos7 data]# swapoff /data/swapfile 
[root@centos7 data]# dd if=/dev/zero of=/data/swapfile bs=1M count=200
200+0 records in
200+0 records out
209715200 bytes (210 MB) copied, 3.23377 s, 64.9 MB/s
# 建立文件系統
[root@centos7 data]# mkswap swapfile 
Setting up swapspace version 1, size = 204796 KiB
no label, UUID=79d0f287-c998-42d3-aabc-b3b2d60b9cb2
# 執行swapon -a啓用全部swap
[root@centos7 data]# swapon -a
[root@centos7 data]# free -h
              total        used        free      shared  buff/cache   available
Mem:           1.9G        176M        1.0G         19M        752M        1.6G
Swap:          4.2G         12M        4.2G

6、卸載

# 取消掛載
[root@centos7 data]# swapoff /data/swapfile 
[root@centos7 data]# sed -ri '$d' /etc/fstab 
[root@centos7 data]# mount -a
[root@centos7 data]# rm -f swapfile 
[root@centos7 data]# free -h
              total        used        free      shared  buff/cache   available
Mem:           1.9G        176M        1.2G         19M        547M        1.6G
Swap:          4.0G         12M        4.0G